Tandem cylinder apparatus and method of using same

ABSTRACT

A tandem cylinder arrangement and a method of operating such a cylinder used particularly in valve actuators. Two load plates are provided with fluid acting on each load plate and the tending to move both load plates together. A cavity between the two load plates is isolated from the hydraulic fluid and a vent allows gasses to enter from and to ingress to the cavity.

INTRODUCTION

[0001] This invention relates to a tandem cylinder arrangement and, more particularly, to a tandem cylinder arrangement used for a safety valve actuator.

BACKGROUND OF THE INVENTION

[0002] Generally, there are two types of cylinder and piston rod movements. A double acting cylinder utilises a rod with a piston movable within a cylinder. Hydraulic fluid is pumped to one side of the piston in order to move the piston rod in a first direction. When movement in the opposite direction is desired, hydraulic fluid is pumped to the opposite side of the piston in order to move the piston and the rod in the opposite direction. A single acting cylinder pumps hydraulic fluid to one side of a piston in order to move the piston and its attached rod in a first direction and a spring is generally used to return the rod and piston to its original position.

[0003] In an actuator used to operate a valve, which actuator may fulfil a safety function to shut down oil flow through a pipeline, as for example, when there is a leak in the pipeline, hydraulic fluid is pumped into a fixed inner cylinder with an open end. A load plate is fixed to the open end and is connected to a stem which stem is connected to the valve intended to be closed when desired. At the opposite end of the load plate, a spring plate is fixed to the outside circumference of the cylinder. The hydraulic fluid acts on the load plate and moves the load plate, the attached cylinder and the spring plate downwardly against the force exerted on the spring plate by a compression spring. When the final desired position of the load plate is reached, the valve will ordinarily be maintained in its open position. When it is desired to close the valve, the spring acting on the spring plate will quickly move the load plate, the attached stem and the valve to the closed position when the fluid is released.

[0004] In the actuator according to the described prior art, the hydraulic fluid acts only on the load plate and the force produced on the load plate is directly proportional to the area of the load plate. To increase the force which may be necessary for many applications, either the pressure of the hydraulic fluid or the area of the load plate is required to be increased. There are practical limits to the pressure that can be applied by the hydraulic circuit because of seal considerations and the requirement for manual pumping of the hydraulic circuit under remote conditions where power may not be available. It is difficult to increase the area of the load plate since the size of the actuator is a limiting factor and increasing the size of the actuator may be expensive. It would be beneficial to increase the force produced by the actuator without increasing the length of the actuator.

SUMMARY OF THE INVENTION

[0005] According to one aspect of the invention, there is provided a method of increasing the force applied to an piston rod and cylinder arrangement, said method comprising applying a pressure medium to a first cavity defined by a seal plate of a piston head and a first load plate of a movable cylinder, applying said pressure medium to a second cavity defined by a surface of a second load plate and the inside of said piston head, evacuating gasses from a third cavity defined by a surface of said second load plate and a surface of said seal plate and allowing said movable cylinder to move under said force applied by said pressure medium in said first and second cavities.

[0006] According to a further aspect of the invention, there is provided a method of increasing the force applied to a piston rod and cylinder arrangement used in an actuator for opening and closing a valve, said method comprising applying a pressure medium to a first cavity defined by a seal plate of a piston head and a first load plate of a movable cylinder, applying said pressure medium to a second cavity defined by the upper surface of a second load plate and the inside of said piston head, evacuating gasses from a third cavity defined by the lower surface of said second load plate and the upper surface of said seal plate and allowing said movable cylinder to move under said force applied by said pressure medium in said first and second cavities.

[0007] According to a further aspect of the invention, there is provided a method of increasing the force applied to a piston rod and cylinder arrangement, said method comprising applying a pressure medium to a first cavity defined by a seal plate of a movable piston head and a first load plate of a cylinder, applying said pressure medium to a second cavity defined by the lower surface of a second load plate of said movable cylinder and the inside of said piston head, evacuating gasses from a third cavity defined by the upper surface of said second load plate and the lower surface of said seal plate and allowing said piston head to move under said force of said pressure medium in said first and second cavities.

[0008] According to a further aspect of the invention, there is provided apparatus for enhancing the force applied to a hydraulic or pneumatic cylinder arrangement comprising a piston head, a seal plate associated with said piston head, a first load plate associated with a movable cylinder and being movable with said cylinder, a second load plate movable with said cylinder, a first cavity defined by a volume between said first load plate and said seal plate, a second cavity defined by a volume between said piston head and said second load plate, and a third cavity defined by a volume between said second load plate and said seal plate, said third cavity having a vent to allow the escape of gases from said third cavity during movement of said cylinder and said second load plate.

[0009] According to yet a further aspect of the invention, there is provided apparatus for enhancing the force applied to a hydraulic or pneumatic cylinder arrangement comprising a piston head, a first load plate means associated with a movable cylinder for movement with said cylinder, a second load plate means for movement with said cylinder, a seal plate means for sealing said piston head, a first cavity defined by a volume between said first load plate means and said seal plate means, a second cavity defining a volume between said piston head and said second load plate means, and a third cavity defining a volume between said second load plate means and said seal plate means, said third cavity having a vent means for allowing the escape of gases from said third cavity during movement of said cylinder and said second load plate means.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0010] Specific embodiments of the invention will now be described, by way of example only, with the use of drawings in which:

[0011]FIG. 1 is a diagrammatic isometric and partial cutaway view of an actuator valve used to terminate fluid flow through a pipeline according to the PRIOR ART;

[0012]FIG. 2 is a diagrammatic cutaway view of a single acting hydraulic cylinder used with the actuator valve of FIG. 1 according to the PRIOR ART;

[0013]FIG. 3 is a diagrammatic cutaway view of a single acting hydraulic cylinder according to one embodiment of the invention which is intended to be used with the valve illustrated in FIG. 1; and

[0014]FIGS. 4A and 4B are diagrammatic cutaway and side views of an actuator according to further embodiments of the invention.

DESCRIPTION OF SPECIFIC EMBODIMENT

[0015] Referring now to the drawings, a valve actuator according to the prior art is generally illustrated at 100 in FIG. 1. The value actuator 100 is used as a part of an emergency shut down system for a gate valve 101 which gate valve 101 may be mounted on a pipeline (not shown). If an emergency occurs because of a leak in the pipeline, for example, the valve actuator 100 will immediately close the gate valve 101 under the influence of a compression spring 105 and terminate flow through the line. The use of such actuators 100 is well known.

[0016] The hydraulic cylinder and its associated parts which are relevant to the operation of the actuator 100 (FIG. 1) are shown more clearly in FIG. 2. The actuator assembly generally illustrated at 120 includes an indicator rod 102 which is connected to a load plate 103, which load plate 103 is fixed to the lower end of a movable cylinder 104. A spring plate 110 is fixed to the opposite or upper end of the cylinder 104. The spring plate 110 bears on a compression spring 111 within an actuator cylinder 112. A stem rod (not illustrated) is threadedly connected to the lower end of indicator rod 102 and extends downwardly to the gate valve 101 (FIG. 1).

[0017] In use, hydraulic fluid is pumped into the interior of the actuator assembly 120 by movement of pump handle 233 (FIG. 1) through inlet 113 and enters the interior of the piston head 114 to act on the upper face of load plate 103. The piston head 114 remains in its fixed position but the load plate 103 and the cylinder 104 will move downwardly under the influence of the hydraulic pressure together with the spring plate 110 which compresses compression spring 111. The downwardly movement will continue until the lowermost position of the load plate 103 is reached at which time the stem rod connected to the load plate 103 will have wholly opened the gate valve 101 (FIG. 1).

[0018] When it is desired to quickly close the gate valve 101, the pressure on the load plate 103 by the hydraulic fluid will be released and the actuator 120, under the influence of compression spring 111, will quickly close the gate valve 101 thereby preventing fluid flow though the gate valve 101.

[0019] Reference is now made to FIG. 3 wherein an actuator assembly according to one aspect of the present invention is generally illustrated at 200. The actuator assembly 200 includes a piston head 201 which is fixed within the actuator assembly 200. The piston head 201 is sealingly isolated by a seal plate 202 which is connected to the lower end of the piston head 201 and which also acts on the indicator rod assembly 203. The indicator rod assembly 203 has a hollow central passageway 204 and a hole 210 drilled into the passageway 204 from the outside circumference of the indicator rod assembly 203 allows ingress and egress of the fluid. The hollow central passageway 204 terminates in an exit passageway 230 extending to the outside of the indicator rod assembly 203. Exit passageway 230 allows hydraulic fluid into a first cavity 240 defined by the lower surface of seal plate 202 and the upper surface of a first load plate 212.

[0020] A second load plate 211 is fixed to the upper area of indicator rod assembly 203 and is in a sealing relationship with the piston head 201. Second load plate 211 is movable with the indicator rod assembly 203 relative to the piston head 201 for the length of the stroke of the indicator rod assembly 23 within the piston head 201.

[0021] First load plate 212 is fixed to and in a sealing relationship with one end of a movable cylinder 213. First load plate 212 has a threaded connection 243 which enables a stem (not illustrated) to be connected and which stem extends to the gate valve 101 (FIG. 1).

[0022] A spring plate 214 is fixed to the outside of the cylinder 213 at the end opposite to first load plate 212 by use of a retainer ring 220. Spring plate 214 abuts the top of compression spring 221 and compresses the compression spring 221 when the cylinder 213 moves downwardly. Following the opening of the gate valve 101 (FIG. 1) by the stem connected to the first load plate 212 when the first load plate 212 is in its most downwardly position, the spring 221 will act on the spring plate 220 when the hydraulic pressure maintaining the gate valve 101 in its open position is released thereby quickly moving the spring plate 214 and the stem upwardly and closing the gate valve 101.

[0023] An inlet passageway 221 is provided for the entrance of pumped hydraulic fluid into a first cavity 222 defined by second load plate 211 and piston head 201. A vent 223 is provided in the piston head 201 which allows air egress from and air ingress to a third cavity 224 defined by the second load plate 211 and the seal plate 202.

OPERATION

[0024] In operation, it will initially be assumed that the gate valve 101 (FIG. 1) is intended to be opened thereby to offer no barrier to fluid traveling through the gate valve 101.

[0025] Using a pump handle 233 (FIG. 1), hydraulic fluid is pumped under pressure from the pump 231 into inlet passageway 221. The hydraulic fluid entering inlet passageway 221 will pass through the inlet passageway 221 until the circumference around the indicator rod assembly 203 is reached. A set of seals 232 is provided between the indicator rod assembly 203 and the piston head 210 and, accordingly, the hydraulic fluid will travel downwardly about the circumference of the indicator rod assembly 203 until it enters the cavity 222 whereupon the fluid acts in the cavity 222 and on second load plate 211 thereby tending to move the indicator rod assembly 203 and the attached cylinder 213 downwardly relative to seal plate 202 and piston head 201 with vent 223 allowing for the release of any air or fluid which may find itself within cavity 224. The hydraulic fluid also enters into hollow central passageway 204 of actuator rod assembly 203 by way of hole 210 and exits the central passageway through exit passageway 230 into cavity 240 defined by the volume between the seal plate 202 and the first load plate 212. Piston head 201 has seals 234 acting between it and the inside diameter of cylinder 213 and, likewise, load plate 212 is sealed against the cylinder 213 with a ring seal 240. Accordingly, the hydraulic fluid exiting from exit passageway 230 will act in the cavity 240 between the first load plate 202 and the first load plate 212 and provides additional downwardly directed force on load plate 212 which also tends to move the attached cylinder 13 downwardly.

[0026] Thus, it will be seen there is an increased force acting to move the indicator rod assembly 203 and connected cylinder 213 downwardly against the force of the compression spring 221 thereby opening the gate valve 101 (FIG. 1). This increased force on the cylinder 213 and indicator rod assembly 203 allows for a reduction in the size of the actuator assembly 200 while still obtaining the same or greater force tending to open the gate valve 101.

[0027] The final or latched position of the open gate valve 101 is reached with the cylinder 213 in the fully down position and with the gate valve 101 being fully open.

[0028] If it is next desired to allow the gate valve 101 to shut the pipeline in which the gate valve 101 is mounted because of an emergency condition or otherwise, the hydraulic fluid in cavities 222, 240 is released thereby removing any bias on the gate valve 101 to remain open. The cylinder 213 and its load plate 212 move upwardly with the stem connected to the gate valve 101 under the influence of compression spring 221 until the cylinder 213 reaches its fully upwardly located position at which time the gate valve 101 is in the fully closed position thereby preventing the flow of fluid through the gate valve 101. Any gases or fluid within cavity 224 are vented through vent 223.

[0029] A further embodiment of the invention is illustrated in FIGS. 4A and 4B. In this further embodiment, the teachings of the invention may necessarily be useful without utilising a spring or indicator rod as were present in the early described embodiment. Referring to FIG. 4A, hydraulic fluid enters the actuator generally illustrated at 300 through an inlet 301 to a first cavity 302 defined by the inside of piston head 303 and the upper surface of a second load plate 304. They hydraulic fluid enters into a central passageway 310 and exits from the passageway 310 into first cavity 311 defined by the bottom surface of seal plate 312 and the inside surface of cylinder 313. Air or fluid is allowed to exit from a third cavity 314 through a vent 320. Force is applied within the first and second cavities 311, 302, respectively, which will move the piston assembly 321 and the attached cylinder 322 downwardly as viewed by the arrows shown in FIG. 4A

[0030]FIG. 4B is similar to FIG. 4A except that the assembly is inverted and whereas the piston head 303 remained stationary in the FIG. 4A embodiment with a moving cylinder 322, the cylinder 322 in the FIG. 4B embodiment remains stationary and the piston head 303 moves relative to the piston head 303 as indicated by the arrows in FIG. 4B.

[0031] Many modifications will readily occur to those skilled in the art to which the invention relates. For example, although hydraulic oil has been referred to as the fluid used throughout the specification, the teachings of the invention would equally apply to other types of fluid used and, indeed, to pneumatic cylinders as well so the invention is useful with any pressure medium. Further, while the teachings of the invention have been described specifically in association with actuators used for opening and closing a gate valve, there are other piston and cylinder arrangements used in applications to which the teachings of the present invention would be beneficial and it is therefore intended to cover such other applications.

[0032] While the piston head 201 is described as being held in fixed position with the cylinder 213 being movable relative thereto, it is apparent that the cylinder 213 could instead be held stationary with the piston head 201 being movable relative to the cylinder 213 as indeed described above in connection with the FIG. 4B embodiment.

[0033] Accordingly, while specific embodiments of the invention have been described, such descriptions should be taken as illustrative of the invention only and not as limiting its scope as defined in accordance with the accompanying claims. 

I claim:
 1. Method of increasing the force applied to an piston rod and cylinder arrangement, said method comprising applying a pressure medium to a first cavity defined by a seal plate of a piston head and a first load plate of a movable cylinder, applying said pressure medium to a second cavity defined by a surface of a second load plate and the inside of said piston head, evacuating gasses from a third cavity defined by a surface of said second load plate and a surface of said seal plate and allowing said movable cylinder to move under said force applied by said pressure medium in said first and second cavities.
 2. Method as in claim 1 wherein said piston rod and cylinder arrangement is an actuator.
 3. Method as in claim 2 wherein said pressure medium is a fluid.
 4. Method as in claim 3 wherein said pressure medium is hydraulic fluid.
 5. Method as in claim 2 wherein said pressure medium is a gas.
 6. Method as in claim 2 wherein said movable cylinder is connected to an indicator rod.
 7. Method as in claim 1 wherein said piston rod and cylinder arrangement is single acting.
 8. Method as in claim 1 wherein said piston rod and cylinder arrangement is double acting.
 9. Method of increasing the force applied to a piston rod and cylinder arrangement used in an actuator for opening and closing a valve, said method comprising applying a pressure medium to a first cavity defined by a seal plate of a piston head and a first load plate of a movable cylinder, applying said pressure medium to a second cavity defined by the upper surface of a second load plate and the inside of said piston head, evacuating gasses from a third cavity defined by the lower surface of said second load plate and the upper surface of said seal plate and allowing said movable cylinder to move under said force applied by said pressure medium in said first and second cavities.
 10. Method as in claim 9 wherein said pressure medium is a fluid or a gas.
 11. Method as in claim 10 wherein said fluid is hydraulic fluid.
 12. Method as in claim 10 wherein said gas is air.
 13. Method as in claim 9 wherein said piston and cylinder arrangement is pneumatic or hydraulic.
 14. Method of increasing the force applied to a piston rod and cylinder arrangement, said method comprising applying a pressure medium to a first cavity defined by a seal plate of a movable piston head and a first load plate of a cylinder, applying said pressure medium to a second cavity defined by the lower surface of a second load plate of said movable cylinder and the inside of said piston head, evacuating gasses from a third cavity defined by the upper surface of said second load plate and the lower surface of said seal plate and allowing said piston head to move under said force of said pressure medium in said first and second cavities.
 15. Method as in claim 14 wherein said piston rod and cylinder arrangement is used with an actuator.
 16. Apparatus for enhancing the force applied to a hydraulic or pneumatic cylinder arrangement comprising a piston head, a seal plate associated with said piston head, a first load plate associated with a movable cylinder and being movable with said cylinder, a second load plate movable with said cylinder, a first cavity defined by a volume between said first load plate and said seal plate, a second cavity defined by a volume between said piston head and said second load plate, and a third cavity defined by a volume between said second load plate and said seal plate, said third cavity having a vent to allow the escape of gases from said third cavity during movement of said cylinder and said second load plate.
 17. Apparatus as in claim 16 wherein said cylinder arrangement is an actuator used to open and close a valve.
 18. Apparatus as in claim 17 wherein said first load plate is separate from and fixed to said movable cylinder.
 19. Apparatus as in claim 17 wherein said seal plate is separate from and fixed to said piston head.
 20. Apparatus as in claim 17 wherein said second load plate is movable within said piston head and fixed to an indicator rod.
 21. Apparatus as in claim 20 wherein said indicator rod moves with said movable cylinder.
 22. Apparatus for enhancing the force applied to a hydraulic or pneumatic cylinder arrangement comprising a piston head, a first load plate means associated with a movable cylinder for movement with said cylinder, a second load plate means for movement with said cylinder, a seal plate means for sealing said piston head, a first cavity defining a volume between said first load plate means and said seal plate means, a second cavity defining a volume between said piston head and said second load plate means, and a third cavity defining a volume between said second load plate means and said seal plate means, said third cavity having a vent means for allowing the escape of gases from said third cavity during movement of said cylinder and second load plate means.
 23. Apparatus as in claim 22 wherein said hydraulic or pneumatic cylinder arrangement is an actuator. 